Typically, the life of a bearing is affected greatly by a preload applied to the bearing, and when a proper preload that is changed depending on a rotating speed and a use condition is applied, it is possible to attenuate the load and variation of a driving shaft.
A bearing assembly is basically configured in such a manner that a proper preload is applied to ensure the rigidity of the driving shaft which is suitable for the use conditions, but, for the reason described above, it is appropriate for the preload to be applied suitably for the use conditions according to the load of the driving shaft and the high-speed or low-speed rotation.
In particular, a constant preload is usually applied to a bearing supporting the driving shaft of a vehicle, and thus a load applied to the driving shaft when the vehicle is empty or full (when cargo is loaded or passengers have boarded the vehicle) is relatively large and a large amount of fuel is consumed. Specifically, a fixed preload is applied to a bearing of a driving shaft system of a conventional vehicle, so that it is possible to suppress the vibration of the driving shaft while accurately positioning the driving shaft in the axial direction and radial direction, and to enhance the rigidity of the bearing. Such a fixed preload applied to the bearing may act on the driving shaft of the vehicle at a constant load, and thereby may cause a problem of increasing the fuel consumption when the vehicle is empty or full.
In this regard, conventionally, the fixed preload of the bearing mounted on an axle is relatively reduced, but in this case, the support force of a tire wheel assembly supported by the axle is reduced, which partially wears down a tire and makes it difficult to achieve stability in toe-in or camber for the steering of the vehicle. When the fixed preload applied to the inner wheel or outer wheel of the bearing is reduced, the tire assembly supported by the axle through the bearing cannot be supported by the axle in an orthogonal direction and vibration is caused by the axle, which makes traveling characteristics unstable.